The present invention is directed to the removal and repair of tissue, particularly to the treatment or removal of tissue by laser ablation, and more particularly to a laser ablation device combined with an optical coherence domain reflectometry (OCDR) unit to provide an image of the ablation area, particularly in front of the ablation surface, whereby the laser ablation device can be safety guided by a user or can be shut off if too close to sensitive tissue.
Laser tissue ablation has been used for many years in medicine and is now starting to find important applications in dentistry. Laser ablation offers the potential of precision cutting with minimal collateral damage and with coagulation. Lasers have been used with good results to cut soft tissue (muscle, fat, cornea) and hard tissue (teeth, bone). However, a need has existed for some form of control mechanism that could control laser ablation and if necessary stop it before causing tissue damage. Prior approaches to this need has been the use of fluorescence spectroscopy or other optical techniques but these prior techniques only probe near the surface and have little sensitivity to tissue type below the surface.
The present invention provides a solution to the above mentioned need by providing a laser ablation device which can either image for a user the surface area and an area in front of the surface area or function to shut off the laser when a certain distance from sensitive tissue (nerve or artery) is determined. Basically, the present invention involves a laser ablation unit, which indudes a high power laser, an optical coherence domain reflectometry (OCDR) unit, and a control unit.
As known in the art, optical coherence domain reflectometry (OCDR) is a technique developed by Younquist et al. in 1987 (Youngquist, R. C. et al., xe2x80x9cOptical Coherence-Domain Reflectometry: A New Optical Evaluation Technique,xe2x80x9d 1987, Optics Letters 12 (3):158-160). Danielson et al. (Danielson, B. L. et al., xe2x80x9cGuided-Wave Reflectometry with Micrometer Resolution,xe2x80x9d 1987, Applied Physics 26(14): 2836-2842) also describe an optical reflectometer which uses a scanning Michelson interferometer in conjunction with a broadband illuminating source and cross-correlation detection. OCDR was first applied to the diagnosis of biological tissue by Clivaz et al. in January 1992 (Clivaz, X. et al., xe2x80x9cHigh-Resolution Reflectometry in Biological Tissues,xe2x80x9d 1992, Optics Letters 17(1):4-6). A similar technique, optical coherence tomography (OCT), has been developed and used for imaging with catheters by Swanson et al. in 1994 (Swanson, E. A. et al., U.S. Pat. Nos. 5,321,501 and 5,459,570). Tearney et al. (Tearney, G. J. et al., xe2x80x9cScanning Single-Mode Fiber Optic Catheter-Endoscope for Optical Coherence Tomograph,xe2x80x9d 1996, Optics Letters 21(7):543-545) also describe an OCT system in which a beam is scanned in a circumferential pattern to produce an image of internal organs. U.S. Pat. No. 5,570,182 to Nathel et al. describes method and apparatus for detection of dental caries and periodontal disease using OCT. However, as OCT systems relay on mechanical scanning arms, miniaturizing them enough to leave room for other devices in the catheter is a serious problem.
Polarization effects in an OCDR system for birefringence characterization have been described by Hee et al. (Hee, M. R. et al., xe2x80x9cPolarization-sensitive low-coherence reflectometer for birefringence characterization and ranging,xe2x80x9d J. Opt. Soc. Am. B, Vol. 9, No. 6, June 1992, 903-908) and in an OCT system by Everett et al. (Everett, M. J. et al., xe2x80x9cBirefringence characterization of biological tissue by use of optical coherence tomography,xe2x80x9d Optics Letters, Vol. 23, No. 3, Feb. 1, 1998, 228-230).
In a prior art OCDR scanning system 10, shown in FIG. 1, light from a low coherence source 12 is input into a 2xc3x972 fiber optic coupler 14, where the light is split and directed into sample arm 16 and reference arm 18. An optical fiber 20 is connected to the sample arm 16 and extends into device 22, which scans an object 24. Reference arm 18 provides a variable optical delay. Light input into reference arm 18 is reflected back by reference mirror 26. A piezoelectric modulator 28 maybe induded in reference arm 18 with a fixed mirror 26, or modulator 28 may be eliminated by scanning mirror 26 in the Z-direction. The reflected reference beam from reference arm 18 and a reflected sample beam from sample arm 16 pass back through coupler 14 to detector 30 (including processing electronics), which processes the signals by techniques that are well known in the art to produce a backscatter profile (or xe2x80x9cimagexe2x80x9d) on display 32.
The potential of the OCDR guided laser ablation device of this invention has been experimentally demonstrated to provide the potential for a range of clinical applications including OCDR guided caries ablation, OCDR guided treatment of periodontal diseases, and OCDR guided surgery.
It is an object of the present invention to provide an improved laser ablation device for both soft and hard tissue.
A further object of the invention is to provide a device for imaging both the surface of a laser ablation area and an area in front of the ablation surface.
A further object of the invention is to provide an optical coherence domain reflectometry (OCDR) guided laser ablation device.
Another object of the invention is to provide a device which combines the effectiveness of laser ablation with an imaging device to enable a user to visualize the tissue in front of an ablation surface.
Another object of the invention is to provide an improved laser application device which combines the use of a high power laser, an OCDR unit, and a control unit, whereby the tissue in front of the ablation surface may be imaged by a user or analyzed to initiate an alarm or shut off the laser when a predetermined distance from the ablation surface to sensitive tissue (e.g., nerve, artery, etc.) is reached, or in dentistry when the diseased enamel or dentin in the caries has all been removed.
Other objects and advantages of the present invention will become apparent from the following description and accompanying drawings. Basically the invention involves an OCDR guided laser ablation device. The invention includes a multimode laser ablation fiber or tool that is surrounded by a plurality of (or only one) single mode optical fibers, the ablation fiber is operatively connected to a high power laser and the optical fibers are operatively connected to an OCDR unit, the high power laser and OCDR unit being connected to a control unit. The optical fibers function via the OCDR unit to image the ablation area, which includes the ablation surface and the areas in front of the ablation surface, that front area being 3 mm deep for example. The surrounding 1, 2, 4 or more single mode optical fibers independently couple light from the sample arm of the OCDR to the tissue being or to be ablated. Light from these fibers exit the tip and are directed into the hard or soft tissue via small diameter optics (such as gradient index lenses and prisms). The light reflected or back-scattered from the tissue is then collected by the same optical fibers and detected by the OCDR unit. This detected information is translated into a profile image of the tissue optical properties near the ablation surface. This information can be displayed on a monitor for the users visual observation or analyzed by computer software to sound an alarm or stop the ablation laser when a selected boundary or distance to sensitive tissue is reached. The device of this invention could use multiple OCDR units (one for each imaging fiber, or used with a form of multiplexer. Thus, the device could be set to sound an alarm or be turned off when the ablation surfaces reaches within 500 microns of an artery wall, for example, or in dentistry when the diseased enamel or dentin in the caries has all been removed. Thus, the present invention has a range of clinical applications including OCDR.